Although database programmers usually focus on relational databases such as Access, Oracle, and SQL Server, object databases can also be useful, particularly for object-oriented architectures. This article shows how to use Visual Basic and XML to build a simple object database.

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What Are Object Databases?

Different kinds of databases are useful for different purposes. A relational
database such as Oracle or SQL Server is convenient when you want to join
records from multiple tables, and tabulate or summarize data. A hierarchical
database is handy when the data you are modeling is naturally hierarchical, as
it is in a directory file system or company organizational chart.

An object database is useful when your program needs to store and
manipulate objects. It provides features you can use to load, examine,
transform, and save those objects.

Typically, an object database lets you locate objects using some sort of key.
For example, the following statement might fetch a Pupil object that
has the key value "Rod Stephens".

pupil = ObjectDatabase.LoadPupil("Rod Stephens")

The program could manipulate the Pupil object, possibly associating
test scores with the object. The program could then explicitly update the
database's representation of this object. Alternatively, the database might
automatically update the object when it was destroyed.

The database would also provide other simple features to perform such
operations as creating a new object, making copies of an object, and deleting an
object.